1. Field of the Invention
The invention relates generally to blowout preventers forming a part of well drilling equipment as used for example in the drilling of bore holes for oil and gas. More particularly this invention relates to a sealing or packing element for a ram-type blowout preventer where the seal element is compressed about a pipe or other object in the bore hole and where the element may accommodate a range of pipe diameters.
2. Description of the Prior Art
In the past, ram-type blowout preventers were provided in stacks such that each individual ram could effectively seal about a different size of pipe or other object extending through the preventer that might be used during the drilling operation. As a result, it had been normal practice to keep several sets of ram blowout preventers on hand and to change the ram size each time the pipe size was changed during the drilling operation. This changing of the ram and the providing of the various ram sizes was inconvenient, expensive and time-consuming. If the blowout preventer stack were relatively inaccessible as in offshore drilling, it became necessary to include several blowout preventers in the stack so that several different pipe sizes used in the drilling of the well could be properly sealed.
U.S. Pat. No. 4,229,012 describes the technological history as presented in issued U.S. patents of prior attempts to provide ram-type blowout preventers having variable bore sealing capability. That patent discusses the difficulties encountered in the prior attempts and discloses a ram blowout preventer with a packer element of a deformable material having reinforcing elements including top and bottom flanges connected by a rib and embedded in the packer or sealing element to reinforce the assembly and prevent longitudinal extrusion of the deformable material under high pressures. Side sealing elements at each side of the packer recesses are disclosed which provide a reservoir of deformable material during the sealing operation. The steel support elements disclosed in the patent rotate inwardly much like the shutter elements in a camera during a packer or ram seal off. It is believed that this movement creates unnecessary degrees of stress in the sealing elements which can potentially create wear for a relatively short life expectancy.
U.S. Pat. No. 4,332,367 represents another attempt at creating a variable ram sealing element by providing a packer with a semi-circular main body and flange sections with embedded support elements having top and bottom plates interconnected by means of a rib or web material. The plates are placed in a semi-circular ring and along the flange sections and are spaced apart from one another to allow movement of the flanges as the packer element is compressed into the bore about a pipe or other object.
There has been described in the technical literature a variable diameter ram with a packer having interlocking "I" beam inserts molded into the rubber. The inserts contain rubber extrusion during seal off between the ram packer and the drill pipe. The nominal or relaxed diameter of the packer is provided intermediate the operating range for which the packer is designed to seal off. During seal off on small diameter drill pipe, the inserts move toward the drill pipe. When a large diameter drill pipe is in the ram bore, the inserts are compressed into the packer by the pipe thus providing automatic adaptation to the pipe size during ram closure and sealing off around the pipe. Under high pressures, the rubber has a tendency to extrude via the channels between the "I" beams thereby limiting the useful life of the packer.
It is an object of this invention to provide an improved packer assembly for a ram blowout preventer having a nominal diameter intermediate the operating range for pipes about which the packer element will seal for automatic adaptation to the pipe size that is easy to manufacture and reliable in operation.
It is a further object of this invention to provide a variable ram packer which prevents longitudinal extrusion of the resilient sealing material under high pressure conditions.
It is a still further object of this invention to provide a variable ram packer or seal element having support elements which are of simple design and are relatively inexpensive to manufacture.